From what I've understood from conversations is World Creator is already in Meters but there is also a full range clamp to exporting, by default I believe it's off? And meters by default start at sea level (0m) which should be about right for TG.

I did a quick 7m render with no fractal detail, and upped displacement multiplier to 7, which does look more like your preview, however their are weird anomalies in the terrain, which I believe is because the original heightmap is not at the right range for TG, so low ground details are being multiplied with the rest of the terrain beyond what should be their maximum.

Not sure what you mean by the "right range". Terragen doesn't care what resolution or height range is represented in the file, generally. The reason you need to multiply is because this terrain (image) format doesn't have built-in scaling values. .ter does, and others can too (.tif with georef data, i.e. geotiff). EXR can be used too, with meter values instead of 0-1 color values, but that's not a standard.

Anyway I would guess these artifacts are part of the original heightfield. That could easily be checked in e.g. Wilbur (free terrain editor/viewer).

Not sure what you mean by the "right range". Terragen doesn't care what resolution or height range is represented in the file, generally. The reason you need to multiply is because this terrain (image) format doesn't have built-in scaling values. .ter does, and others can too (.tif with georef data, i.e. geotiff). EXR can be used too, with meter values instead of 0-1 color values, but that's not a standard.

Anyway I would guess these artifacts are part of the original heightfield. That could easily be checked in e.g. Wilbur (free terrain editor/viewer).

From what I'm looking at here, compared to a 4k heightmap in TIFF format from the same application, his heightmap is clamped and not full range.

In TIFF format, this will effect the desired scale range because of inherently how TG reads it expecting it to be 0-1 range.

Edit: That being said, small, low scale details will not be appropriately represented in a 0-1 range when clamped in TIFF format. Being barely present and/or clamped/cut off, they will be exponentially effected by scaling up the terrain in Terragen beyond it's read 0-1 range.